Pavement markings are used extensively to visually delineate portions of a road surface, for example, the edges or center of the road surface. In some applications, the pavement marking is simply a colored mixture. For example, Regenstein et al., U.S. Pat. No. 3,297,617 disclose a coating slurry that can contain various pigments which can be used to mark a road surface. Frequently, retroreflective particles, such as glass beads, are added to pavement markings to improve the visibility of the pavement marking in adverse situations, such as at night. Bollag, U.S. Pat. No. 4,856,931 discloses a pavement marking that is produced by painting a line on the pavement and thereafter scattering glass beads over the painted line while the paint is still tacky. Shuger, U.S. Pat. No. 2,268,537, de Vries, U.S. Pat. No. RE 28,531, La Roche, U.S. Pat. No. 5,128,203, and Rodli et al., U.S. Pat. No. 2,330,843 similarly disclose solvent-based pavement marking mixtures that are applied to the pavement, for example, by spraying. Glass beads are then applied to the mixtures while the mixtures are still semi-wet or tacky. Kullenberg, U.S. Pat. No. 2,879,171 discloses a solvent-based pavement marking mixture that includes glass beads in a stabilized aqueous dispersion.
Pavement marking mixtures using non-solvent based materials have been proposed. La Roche, U.S. Pat. No. 5,128,203 discloses a two component acrylic matrix-forming material that is applied to the pavement. Glass beads are then sprinkled over the applied matrix-forming material within one minute of mixing the acrylic matrix-forming material. La Roche also discloses a pavement marking kit based on a thermoplastic matrix-forming material. The thermoplastic matrix-forming material is heated and applied to the pavement. Glass beads are then sprinkled over the thermoplastic material while it is still liquid. Haenggi et al., U.S. Pat. Nos. 4,937,127, 5,053,253, and 5,124,178 disclose a pavement marking tape that includes a base sheet which has an upper polymer matrix surface. Glass beads are embedded in the matrix surface before it is cured. The final tape product, which includes glass beads, is then affixed to a road surface with an adhesive. Jorgensen et al., U.S. Pat. No. 3,849,351 disclose a particulate pavement marking mixture that includes a thermoplastic phase which consists principally of polyamide condensation products of polycarboxylic acid and polyamine, and glass beads. The pavement marking mixture is applied to a road surface using a flame-applicator.
Conventional pavement marking mixtures suffer from disadvantages. As noted earlier retroreflective particles, such as glass beads, are frequently added to the surface of pavement markings before the pavement marking mixtures have set-up on the road surface. Initially, the surface-added retroreflective particles improve the visibility of the pavement markings. However, the retroreflective particles tend to wear away under traffic and the like. Thus pavement marking mixtures that depend on surface-added retroreflective particles to enhance their visibility lose their retroreflective characteristics over time, also relatively long application times are required for solvent-based pavement marking mixtures. Solvent-based pavement marking mixtures generally become set when the solvent evaporates. The amount of time required for the solvent to evaporate varies with the type of solvent used and the solvent-percentage composition. However, drying times on the order of 15 to 60 minutes are not unusual. Consequently, pavement markings formed from solvent-based pavement marking mixtures frequently must be protected from traffic for relatively long periods. The setting time for solvent-based mixtures thus restricts traffic flow and increases the cost of using such mixtures.
Conventional thermoplastic-based pavement marking mixtures suffer from additional disadvantages. Conventional thermoplastic-based pavement marking mixtures generally are marketed as heterogeneous mixtures of individual, raw components. Consequently, the end-user must mix together the raw components at elevated temperatures for significant time periods before the pavement marking mixture is ready to be applied to a road surface. The raw components generally do not remain evenly pre-mixed, because they tend to form loose mixtures which become segregated during shipping and handling. Mixing and melting of the unevenly distributed particles is slower, resulting in extended mixing times and variable temperature requirements, which increase the cost of applying the mixture to a road surface and thus increase the cost of using such mixtures.